The macrophage specific mannose fucosyl receptor is a lectin-like receptor which recognizes mannose and fucose containing ligands found in bacterial cell walls, yeasts and parasites. Engagement of the receptor at the cell surface leads to the active release of a variety of biologically active molecules involved in tumoricidal and microbicidal activity, homeostasis and inflammation, including several neutral proteinases and products derived from arachidonate and oxygen. Mannose fucosyl receptor expression is a sensitive indicator of the functional state of the macrophage. The high levels found in non-activated and inflammatory macrophages can be further increased two to threefold by interferons alpha and beta. Interestingly interferon gamma, a macrophage activating factor which induces the enhanced ability of the macrophage to release reactive oxygen metabolites which account for most (though not all) of the antimicrobial and tumoricidal activity, decreases the expression of the mannose fucosyl receptor. The decreased expression of the mannose fucosyl receptor is a sensitive and highly reproducible indicator of the co-ordinate changes which are induced by interferon gamma in man and mouse. We believe that the mannose fucosyl receptor gene, unlike other genes which are regulated by interferons, is an attractive model to study the effects of interferons on gene regulation as it is uniquely regulated by interferons. We have isolated a cDNA clone which corresponds to a macrophage restricted mRNA of 5kb from a lambda gtll 7d human monocyte cDNA library which we prepared, using a specific anti MFR anisera. The abundance of this specific mRNA is decreased in MO which have been exposed to interferon gamma. We will prove that this cDNA clone encodes for the MFR protein by 1) obtaining MFR protein sequence 2) performing hybrid arrest translation using MFR cDNA as a template 3) preparing heteroantisera and monoclonal antibodies to putative MFR fusion proteins and synthetic peptides. As we believe that structural information should precede experimental work directed towards understanding the regulation of the gene, we will characterise the primary sequence and gene structure by analysing full length cDNA and genomic clones. We will express these clones in mammalian cells to establish functional assays to study the effects of interferons on MFR gene expression. Our ultimate aim is to utilise the structural data of MFR gene to isolated interferon responsive regulatory sequences. We believe that this is an experimentally attractive model to study the mechanism of interferon action on gene control and we hope that this will eventually be of practical value in developing selective agents which can modulate macrophage function.